OTop 8 questions....

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Bill Fitzmaurice
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Re: OTop 8 questions....

#16 Post by Bill Fitzmaurice » Sun Oct 29, 2017 11:24 am

It's no secret that horns are bandpass devices, and that the response of a driver as a direct radiator bears no resemblance whatsoever to its response when horn loaded.

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Re: OTop 8 questions....

#17 Post by Think » Sun Oct 29, 2017 12:30 pm

Bill Fitzmaurice wrote:It's no secret that horns are bandpass devices, and that the response of a driver as a direct radiator bears no resemblance whatsoever to its response when horn loaded.
So the horn is not effective for the higher frequenties the driver can produce?

And the more technical explanation would be the throat of the horn is to big (wild guess) to be effective for the 3-4kHz range?

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Re: OTop 8 questions....

#18 Post by Bill Fitzmaurice » Sun Oct 29, 2017 3:13 pm

The chamber between the cone and throat is a low pass filter. Also, where the throat dimension is more than one wavelength there is no gain.

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Re: OTop 8 questions....

#19 Post by Think » Mon Oct 30, 2017 9:57 am

Thank you this info, it gives me a better understanding of how the speaker works.
Bill Fitzmaurice wrote: .... and that the response of a driver as a direct radiator bears no resemblance whatsoever to its response when horn loaded.
This puzzles me, as with the PA 12 Top a driver with a rising mids (1-2kHz) is recommended. Is there a resemblence in response as long as it is in the bandpass of the horn?

Or is it just 'coincidence' that drivers like the beta12a, 2512, 3012lf have rising mids in a open baffle, direct radiator box and in a horn?

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Re: OTop 8 questions....

#20 Post by Bill Fitzmaurice » Mon Oct 30, 2017 10:39 am

Think wrote:is it just 'coincidence' that drivers like the beta12a, 2512, 3012lf have rising mids... in a horn?
They don't. We use them because their rising response helps to compensate for the horns effect on midrange response.

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Re: OTop 8 questions....

#21 Post by madmallard » Mon Oct 30, 2017 5:43 pm

Bill Fitzmaurice wrote:The OTop 8 is now available.
http://www.billfitzmaurice.com/OmniTop% ... 20Top.html

Loaded with two 8 inch woofers, and either a straight or melded piezo array or dual compression drivers, this is our narrowest fully horn loaded PA top. They can be used singly or stacked in a line array or spiral array. Performance is roughly equal to the DR200, but at 16 inches wide it's 4 inches narrower than the DR200, 6 inches narrower than the OTop 12.
playing the fool, here, so pardon me.

But if the performance is similar to the DR200 and by your account the DR200 is a more complicated cabinet to build by double difficulty (and combined with the smaller form factor), what circumstances should one be building the DR200?

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Re: OTop 8 questions....

#22 Post by Bruce Weldy » Mon Oct 30, 2017 6:00 pm

madmallard wrote:
Bill Fitzmaurice wrote:The OTop 8 is now available.
http://www.billfitzmaurice.com/OmniTop% ... 20Top.html

Loaded with two 8 inch woofers, and either a straight or melded piezo array or dual compression drivers, this is our narrowest fully horn loaded PA top. They can be used singly or stacked in a line array or spiral array. Performance is roughly equal to the DR200, but at 16 inches wide it's 4 inches narrower than the DR200, 6 inches narrower than the OTop 12.
playing the fool, here, so pardon me.

But if the performance is similar to the DR200 and by your account the DR200 is a more complicated cabinet to build by double difficulty (and combined with the smaller form factor), what circumstances should one be building the DR200?
Size, weight, ability for form an angled array.....different strokes....

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Bill Fitzmaurice
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Re: OTop 8 questions....

#23 Post by Bill Fitzmaurice » Mon Oct 30, 2017 9:14 pm

Bruce Weldy wrote: Size, weight, ability for form an angled array.....different strokes....
That, plus DR200 uses one eight, Top 8 uses two eights. Output of the two is about the same, but the OTop needs twice the power to deliver it. The more efficient design of the DR200 is a more difficult build, but has its advantages. I've long said that if you can build a DR you should, if you can't, build an OTop. That still applies, with the only additional factor being that the OTop 8 is narrower than the DR200. Where that's concerned the OTop 8 came about in response to a specific request from one of our authorized builders for a horn loaded top as narrow as possible.

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Re: OTop 8 questions....

#24 Post by Think » Thu Nov 02, 2017 12:44 am

Bill Fitzmaurice wrote:
Bruce Weldy wrote: Size, weight, ability for form an angled array.....different strokes....
.....OTop 8 is narrower than the DR200. Where that's concerned the OTop 8 came about in response to a specific request from one of our authorized builders for a horn loaded top as narrow as possible.
If you would rotate the OmniTop12 90 degrees and make some adaptations like the relocation of the reflex ports, mountingpost and tweeters etc, would the off axis performance suffer to much?
Or are there other reasons that would not work?

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Re: OTop 8 questions....

#25 Post by Tom Smit » Thu Nov 02, 2017 12:49 am

Rotating the OTop12 90degrees would narrow the dispersion immensely.
TomS

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Re: OTop 8 questions....

#26 Post by djlivex » Thu Nov 23, 2017 1:17 pm

Bill Fitzmaurice wrote:It doesn't. With the option of series or parallel wiring the woofers I didn't want to make matters any more complicated by specifying 8 ohm HF drivers for parallel wired woofers and 16 ohm HF drivers for series wired woofers. If you find the HF section too hot I can calculate fixed value resistor LPads to add post high-pass. Variable LPads are only available in 8 ohms. Stereo 8 ohm LPads can be wired parallel for 4 ohm loads but there's no way to wire them for 16 ohms.
2 x 1" NSD 2005 will be hot especially Titanium Dia. Well if you parallel the 2 CD's = 8 ohms for the L-Pad? Curious . . . :confused:
BaasssS, . . how low can you GO!

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Re: OTop 8 questions....

#27 Post by djlivex » Thu Nov 23, 2017 2:16 pm

Bill is it possible to use Beta coax then 1" CD in the back eliminating the double horn or piezo array? :(
BaasssS, . . how low can you GO!

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Re: OTop 8 questions....

#28 Post by Bill Fitzmaurice » Thu Nov 23, 2017 2:24 pm

If you do you lose the ability to stack cabs. Besides, it would be too deep to fit into the cab. As for NSD 2005s, if they were a viable option it would be in the plans. There's no need for a driver that goes lower than 2kHz.

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Re: OTop 8 questions....

#29 Post by djlivex » Thu Nov 23, 2017 9:24 pm

Bill Fitzmaurice wrote:If you do you lose the ability to stack cabs. Besides, it would be too deep to fit into the cab. As for NSD 2005s, if they were a viable option it would be in the plans. There's no need for a driver that goes lower than 2kHz.
Oh ok I see it now in the plans that is why you have 2 tophat holes so you can stack another cab with a small pole.

My other question if I use the Faital 8" since it has more Xmax does that mean bigger hole handle?

So you don't really build 2 per side for wider dispersion you stack them on top of each other?

Thanks just going over the plans, seems easy built except of the smaller pieces 1" horn plates. I guess 2 x 1" plastic CD horn cut then

and glued on top of each other ala DR300 wouldn't work? Thinking 4 cabs. 8)

Thanks Bill!
BaasssS, . . how low can you GO!

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Re: OTop 8 questions....

#30 Post by CoronaOperator » Thu Nov 23, 2017 9:31 pm

djlivex wrote: Thanks just going over the plans, seems easy built except of the smaller pieces 1" horn plates.
\

Cutting those smaller pieces is the easy part, it's the gluing them together that will drive you nuts.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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